Hundreds of Southwest Airlines flights were delayed after technical issues led the airline to temporarily halt operations Tuesday morning.

Southwest said the flight delays were the result of “data connection issues resulting from a firewall failure,” an issue that caused a brief ground stop.

The Federal Aviation Administration The ground stop began at the request of the airlineciting “team issues.” Soon the stop was lifted and, in an instant, tweet at 11:35 a.m. ET Southwest said had resumed operations.

“Early this morning, a vendor-provided firewall went down and the connection to some operational data was unexpectedly lost,” spokesman Dan Landson said in a statement.

Southwest had delayed 1,820 flights or 43% of its schedule shortly after noon Tuesday, according to FlightAware. The airline canceled only nine flights on Tuesday, according to FlightAware. Southwest says its workers “worked quickly to minimize disruptions.”

Southwest reported technology issues Tuesday morning and said it would “hopefully resume our operation as soon as possible.”

In a statement, the FAA told CNN that Southwest “requested the FAA to suspend the airline’s departures.”

The problems come months after the airline was forced to cancel more than 16,700 flights between December 20 and 29, about half of its schedule during that period. The airline attributed the crisis in part to changes in its staff’s computer scheduling systems. Last month, Southwest unveiled an “action plan” to avoid another operational collapse.

Southwest called the latest issue “intermittent technology issues” in a social media post to customers. Several took to social media to complain about flight delays.

“We apologize for any inconvenience this may cause, but we hope everyone can get started as soon as possible,” the airline wrote in another social media post.

A massive winter storm kicked off service problems during the holiday season, but Southwest had a harder time recovering due to an antiquated crew scheduling system that quickly became overwhelmed, leaving the airline unable to get the staff it needed on the ground to operate flights. Almost half of its programming was canceled between December 20 and 29. Some days, up to 75% of its scheduled flights were grounded.

Part of what created worse problems at Southwest than other airlines is that crew members had to call the airline, rather than notify it electronically, to inform them of their availability.